Generally, for example, an illumination device which is used for a ceiling light, a headlight or the like of a vehicle can be provided with a PWM (pulse width modulation) control. By controlling the illumination device by the PWM control, for example, the brightness of the load of an illumination unit (which practically illuminates) of the illumination device can be readily changed. Specifically, the brightness can be adjusted by changing a pulse width with respect to one period. Moreover, the illumination unit can gradually become bright or dark, by gradually changing the pulse width into a target pulse width. The control of the pulse width in this case will be called a fade control in the later description.
However, in the case where the load of the illumination unit is supplied with electrical current by the PWM control to be made illuminate (glow), there will occur a violent variation of the current at the time of the pulse rise and the pulse decay. Due to the variation of the current, electromagnetic wave (noise) occurs to adversely affect other electronic components. For example, a malfunction will be caused. Particularly, in the case where the current flowing through the load of the illumination unit is large, the electromagnetic wave will become strong.